Wednesday night will be the peak of the 2010 Leonid meteor shower—but North American sky-watchers hoping to see the Leonids at their best will have to set early morning alarms Tuesday night.
Historically the November Leonids deliver one of the most active of the annual meteor showers. Occasionally the Leonids produce bona fide meteor storms, with rates of a few hundred to thousands of shooting stars an hour during the peak. (Get the scoop on last year's Leonids.)
This year's performance is expected to be modest but still a good sky show, with peak rates of up to 20 meteors an hour.
The best viewing dates for this year will be Wednesday and Thursday, with the official peak occurring on Wednesday at midday in North America, a time slot that favors observers in Asia.
"The meteors will appear to radiate from the constellation Leo, the lion, which rises around midnight in the east," said Raminder Singh Samra, resident astronomer at the H.R. MacMillan Space Centre in Vancouver, Canada.
"Meteor activity should pick up closer to early morning hours [in North America on Wednesday] as the Earth plows through the comet debris" that creates the meteor shower, Samra said. (See asteroid and comet pictures.)
No matter the location, observers will have to contend with the moon, which will be close to full and up for most of the night. That means bright moonlight will wash out many of the fainter meteor trails, Samra said.
But the moon will set a couple hours before sunrise, when the most intense part of the shower should start to kick in, he added.
Modest Leonids May Still Surprise
As with other meteor showers, such as the Perseids in August and the Orionids in October, the Leonids are named for the constellation that appears to be the shower's source. (See Perseids pictures.)
In reality, the Leonids, and most other meteor showers, happen when Earth plows through a trail of debris left in the wake of a comet orbiting the sun—in this case, comet Tempel-Tuttle.
When a comet gets close to the sun, vaporizing ice releases pieces of dust, most no larger than grains of sand. This debris generally settles into the same orbital path as the comet, although the dusty trail can be shifted slightly by gravitational interactions with larger planets, such as Jupiter.
Earth annually crosses through the orbiting debris of some comets, which burns up in our atmosphere and creates meteors. Occasionally a larger object, more like a pebble or even a boulder, will produce a brilliant fireball. (Also see "Exploding Clays Drive Geminids Sky Show?")
"When our planet passes through denser clumps of material, we experience higher meteor rates," said Geza Gyuk, an astronomer at the Adler Planetarium in Chicago. "This year we will only be hitting a normal section of the debris trail, probably leading to lower numbers."
Still, meteor shower forecasts are in their infancy, and predicting exactly how many meteors will light up the sky is relatively hard. (Find out why next October's Draconid meteor shower might be a meteor outburst.)
"Although we are getting better at predicting the structure of the debris stream, and hence the pattern of activity during the shower, the Leonids can still surprise us—so don't give up if the peak times are cloudy," Gyuk said.
"Also keep in mind that the Leonids will produce somewhat elevated rates of meteors the day before the official peak"—as Earth closes in on the densest part of the debris stream—and the day after.